Grinding-mill.



M. J. DAVIDSEN.

GRINDING MILL.

, APPLICATION FILED SEPT. 16, 1907.

98$,Q28, Patented Jan. 31, 1911.

srns

MEYER JOSEPH DAVIDSEN, OF COPENHAGEN, DENMARK, ASSIGNOR TO F. Li SMIDTH & 00., OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY.

GRINDING-MILL.

eeaoas.

Specification of Letters Patent. Patented Jan, 31, 1911.

Application filed September 16, 1907. Serial No. 393,252. i

To all whom it may concern:

Be it known that I, MEYER JOSEPH DAVID- SEN, civil engineer, citizen of Denmark, residing at No. 33 Vestergade, Copenhagen, in the Kingdom of Denmark, have invented new and useful Improvements in Grinding- Mills, of which the following is a speciti cation.

This invention relates to grinding mills in whichthe reduction to a finely powdered condition of coal, ore orother substances is effected by grinding bodies which are placed,

together with the material to be pulverized, in a drum which is rotated at a relatively slow speed. The weight of the material to be powdered and of the grinding bodies,

which together partially fill-the drum, is considerable and the'power required to rotate the drum is therefore considerable. Roughly speaking the h. p. required is measured by the product of the weight of the entire mass into the distance from the axis of the drum to the center of gravity of the mass, the length of the drum being disregarded. Economy in the power consumed,

' therefore, becomes a desideratum, and it is operation, and rectangular blocks of metal having plane surfacesand sharp corners. These attempts have apparentlynotbeen sufficiently successful to bring about any extensive substitution of sugl l bodies for the flint pebbles which are generally used, but in the present invention it has been discovered that the greatest efliciency in such mills is secureo by the employment of grinding bodies which furnish the maximum of sur--' face for thesame weight, and the grinding bodies used in accordance with the invention are therefore comparatively small, cylindrical bodies of any suitable metal. With such bodies it is found that very great fineness of the ground product can be "secured with a saving in h. p. of from forty to fifty per cent, as compared with the use of flint peb bles, in the treatment of such material as clinker and hard bituminous coal. Moreover, it has been found to be possible with such material to treat successfully damp material, such as damp coal, which, under treatment with flint pebbles, is generally ncompacted in scales or flakes which are not thereafter broken up. Among other advantages may be enumerated the following:

The specific gravity of'the grinding bodies being the same, a smaller total weight of grinding bodies may be employed; a reduction in the size-of the machinery employed is possible; a finer reduction of the material can be effected; the small size of the metal grinding bodies permits them to be hardened practically throughout.

In the accompanying drawin in which the invention is illustrated, so far as itis vention, Figure 1 is an outline perspective or diagrammatic View of the cyllnder or drum capable of illustration, for the purpose of indicating visually the character of the inof a grinding mill with its charge of material to be powdered and grinding bodies. F ig. 2 is a perspective view, on a much larger scale, of one of the grinding" bodies.

The cylinder or drum of the grinding mill, indicated at a in the-drawing, may be of any suitable dimensions and may be rotated at the required speed by any suitable means and may be provided with suitable devices for the introduction and removal of the charge. Except for the provision, broadly, of a suitable container in which the material. to be treated and the grinding bodies.

may be made to move together, the construction and arrangement of the mill and its parts are not material to the invention and therefore need not be further illustrated. t The invention is particularly concerned withrtbe size and shape of the grinding. bodies employed. Such grinding bodies, mixed with the material under treatment, are shown in "mass, at b in Fig.1, and one of such parts is shown at c in Fig. 2. As

represented, each of such grinding bodies is'a solid, relatively small cylindrical body.

The precise dimensions of such grinding body, are immaterial, but as an indication of the approximate dimensions it .may be said that for'most purposes highly satisfactory results are obtained with cylindrical grinding bodies which have each a length of about five-eighths of an inch and a diameter of about three-eighths of an inch. The weight of each of such grinding bodies will depend, obviously, more or less upon the material of Which it is made, a suitable average being about twenty grams.

The grinding bodies may be made of rods of iron or steel cut into short lengths, or even of the small cylindrical pieces'which may be stamped out of sheets or plates of metal in the preparation of such plates or sheets for other uses. If desired, these bodies maybe subjected to ahardening process which, on account of the small size of the bodies, hardens them practically through out the mass of it.

I claim as my invention:

A grinding mill comprising a rotary drumin which the material to be ground and the grinding bodies are moved together, and grinding bodies each consisting of a solid cylinder of metal having a length of approximately five eighths of an inch and a diameter of approximately three eighths of an inch. v

In testimony whereof I have signed my name to this specification in the presence of tWo subscribing Witnesses.

J. HoFMANsAY, AXEL PERMIN. 

